The principle of horizontal equity demands that similarly situated individuals face similar tax burdens. It is universally accepted as one of the more significant criteria of a "good tax." It is relied upon in discussions of the tax base, the tax unit, the reporting period, and more. Violation of horizontal equity, while not necessarily fatal, is nevertheless considered a serious flaw in any proposed tax arrangement.
"Horizontal Equity as a Principle of Tax Theory,"
Yale Law & Policy Review:
1, Article 3.
Available at: http://digitalcommons.law.yale.edu/ylpr/vol24/iss1/3